The use of gas turbine engines to drive generators to produce electricity has become increasingly attractive in recent years to meet the varying electrical demands of utility customers. Both simple cycle plants and combined cycle plants are in use. In a simple cycle plant, the engine exhaust gas is routed directly to the atmosphere through the exhaust stack. In a combined cycle plant, a heat recovery steam generator is provided in the engine exhaust gas stream to produce steam, which is used to produce additional electrical power in a steam turbine driven generator. It is desirable to increase the operating efficiency of such plants to meet increasingly competitive market demands.
The operating efficiency of a gas turbine engine driven generation plant may be increased by heating the fuel prior to combustion in the engine as less fuel energy is needed to raise the fuel temperature for combustion. Such plants produce considerable excess heat that may be used to increase the temperature of the fuel. For example, in a conventional combined cycle plant, steam produced in the heat recovery steam generator may be diverted from the steam turbine driven generator to a heat exchanger and used to heat the fuel.
U.S. Pat. No. 5,845,481 discloses a system where engine fuel is heated by passing it through a heat exchanger in a by-pass channel connected to the engine exhaust stack. The amount of exhaust gas passing through the by-pass channel is controlled by a damper, and the exhaust gas is vented to the atmosphere after passing through the by-pass channel. Unheated fuel may be mixed with the heated fuel to control the temperature of the heated fuel before combustion in the engine.